Electronic devices such as wireless terminals often include a keypad for user inputs. As is well known to those having skill in the art, an electronic device typically includes a housing, a plurality of electronic components in the housing and a keypad at least partially in the housing. The keypad includes at least one key.
For example, a wireless terminal generally includes a keypad having a set of number keys (0-9), a * key and a # key, and one or more function keys, such as SEND, END and → keys. As used herein, the term “wireless terminal” encompasses a wide variety of portable or fixed wireless devices that can access a wireless communications system. Wireless terminals include a cellular radiotelephone with a multi-line display, a Personal Communications System (PCS) terminal that may combine a cellular radiotelephone with data processing, facsimile and/or data communications capabilities, a Personal Digital Assistant (PDA) that can include a radiotelephone, pager, Internet/intranet access, Web browser, organizer, calendar and/or a Global Positioning System (GPS) receiver, and conventional laptop, palmtop and/or pervasive computing devices that include wireless receivers.
Electronic devices often are used in poorly lit or dark environments, so that it may be desirable to illuminate the keypads thereof. Moreover, even if the keypad is not illuminated, it may be desirable to illuminate an individual key upon actuation thereof to provide visible feedback. Keypad illumination may present technical challenges for wireless terminals due to the desirability of decreasing the size and decreasing the power consumption of the wireless terminal, while at the same time providing bright, evenly distributed illumination.
It is generally known to illuminate a keypad using Light Emitting Diodes (LEDs) and a lightguide. Some keypad illumination schemes use LEDs to send light into a lightguide that is made of transparent material. The lightguide guides the light until it meets surfaces that are designed to reflect light up through the keys. Other techniques using a lightguide that is made of dispersing (translucent) material, wherein the light is scattered all around and some portion of the light is transmitted out of the lightguide through the keys. Wireless terminals with lightguides are described, for example, in U.S. Pat. No. 6,006,118 to Stephenson, entitled Keypad Lightguides Including Compartments, and U.S. Pat. No. 6,026,283 to Stephenson, entitled Electrically Conductive Keypad Lightguides.
Unfortunately, lightguides may have low optical efficiency due to the desire to make the lightguide thin and/or the desire to provide holes and/or other deformations therein to accommodate other components of the wireless terminal. Moreover, since LEDs may send out light in many directions, efficient optical coupling to the lightguide may be difficult. It also may be difficult to obtain evenly distributed light, so that about the same luminescence may be obtained from all the keys. In order to obtain evenly distributed light, many LEDs may be used, which may increase power consumption and/or cost. Moreover, light may leak from the gap between the keys and the housing.